JP3427643B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine adopting an electrophotographic system.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine which employs an electrophotographic system, it is desired that an image having a constant density is reproduced on a recording paper for the same image data. To meet this demand, in order to reproduce an image of stable density on a recording paper, a reference toner image is formed on the photoconductor before copying is performed or when a predetermined mode is set, and the formed toner is formed. It is known that the transfer efficiency of an image on a recording paper is detected and the developing condition or the transfer condition is controlled based on the detected result.

[0003]

However, in the above-mentioned conventional image forming apparatus, when the toner deteriorates, or when the paper absorbs moisture and the resistance value decreases more than expected, appropriate control is not performed, There is a problem that the transfer efficiency is lowered. For example, when the recording paper absorbs moisture, its resistance value decreases. Therefore, even if the toner is appropriately charged, the toner is reversely charged at the transfer portion, the amount of the toner remaining on the photosensitive drum increases, and as a result, the transfer efficiency decreases. If the toner is deteriorated, the charge amount of the toner after development and before transfer is reduced. As a result, the toner is reversely charged in the transfer portion, the amount of the toner remaining on the photosensitive drum increases, and as a result, the transfer efficiency decreases.

An object of the present invention is to provide an image forming apparatus capable of performing stable transfer regardless of the state of recording paper or toner.

[0005]

[Means for Solving the Problems] The present inventionPicture ofImage forming device
Is an image forming apparatus that employs an electrophotographic method.
Development of forming a reference toner pattern on the photoconductor and the photoconductor
And the reference toner pattern on the photoconductor is transferred to recording paper
Is provided between the photoconductor and the transfer means.
Before the transfer film and the toner image are transferred to the recording paper,
A pre-transfer charger that increases the amount of charge on the toner image,
Between the photoconductor and the transfer means via the transfer film and recording paper
First capacitance between, transfer film, recording paper and reference
Second between the photoconductor and the transfer means via the toner pattern
Of the capacitance of the
According to the determined first and second capacitances, the reference toner
A first calculation means for calculating the capacitance of the pattern;
Of the reference toner pattern calculated by the calculation means of
A first comparing means for comparing the capacity with a first reference value;
Of the reference toner pattern calculated by the calculation unit 1
If it is determined that the capacitance is above the first reference value,
The first to increase the grid voltage of the pre-charger by a predetermined amount
And the control means of. In this image forming apparatus,
The above-mentioned measuring means is transferred to the photoconductor through the transfer film only.
The third capacitance between the copying means is further measured, and the third capacitance is measured.
The capacitance of the recording paper is calculated according to the first and third capacitances.
A second calculation means for calculating and a calculation performed by the second calculation means.
A second comparing the capacitance of the recorded recording paper with a second reference value
And the recording paper calculated by the second calculating means
If the capacitance of is determined to be greater than or equal to the second reference value,
Second, the voltage applied to the transfer means is reduced by a predetermined amount.
It is preferable to further include the control means of. The present inventionNomono
One image forming apparatus is an image adopting an electrophotographic method.
In the forming device, the photoconductor and the reference toner pattern on the photoconductor.
The developing means that forms the turn and the reference toner pattern on the photoconductor.
Transfer means that transfers the turns to the recording paper, and the photoconductor and transfer hand.
The transfer film provided between the step and the toner image is recorded.
Before transferring to paper, the toner image charge amount is increased
Photoreceptor via pre-charger and transfer film only
A first capacitance between the transfer film and the transfer means,
Between the photoconductor and the transfer unit via the reference toner pattern
Measuring means for measuring the second capacitance of
According to the first and second capacitance measured by the
First calculating means for calculating the electrostatic capacity of the toner pattern
And the reference toner pattern calculated by the first calculation means.
A first comparison hand for comparing the capacitance of the battery with the first reference value.
And the reference toner pattern calculated by the first calculating means.
Judging that the capacitance of the battery is greater than or equal to the first reference capacitance
If not, set the grid voltage of the pre-transfer charger to the specified value.
And a first control means for increasing the amount. This image forming device
In the storage, the measuring means is
The third capacitance between the photoconductor and the transfer means via the paper
Further measured, the first and third measured by the measuring means
Second, which calculates the electrostatic capacity of the recording paper according to the electrostatic capacity of
And the recording paper calculated by the second calculating means
Second comparing means for comparing the electrostatic capacitance of the battery with a second reference value
And it is determined that the electrostatic capacity of the recording paper is greater than or equal to the second reference value.
If the voltage is applied, the voltage applied to the transfer means is reduced by a specified amount.
It is preferable to further include a second control means for activating.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION A copying machine as an embodiment of an image forming apparatus of the present invention will be described below in order with reference to the accompanying drawings. (1) Embodiment FIG. 1 is a sectional view of a digital full-color copying machine according to the embodiment. The copying machine includes an image reader unit 100 for reading an image of a document and a printer unit 20 for forming an image on a recording sheet based on the read image data of the document.
It is roughly divided into 0. In the image reader unit 100, the document placed on the document table glass 1 is illuminated by the lamp 3 included in the scanner 2. The reflected light from the document surface is imaged on the CCD line sensor 8 via the mirrors 4, 5, 6 and the imaging lens 7. Scanner 2
Is the direction of the arrow by the scanner motor 10 (sub-scanning direction)
It moves at a speed V according to the set magnification. As a result, the document placed on the document table glass 1 is scanned over the entire surface. Further, the mirrors 5 and 6 also move in the arrow direction (sub-scanning direction) at the speed V / 2 as the scanner 2 moves. R, G, obtained by the CCD line sensor 8
The multivalued electrical signal of B is converted into 8-bit gradation data by the read signal processing unit 9 and then output to the printer unit 200. An operation panel 5 for setting the number of copies and executing the copy is provided on the image reader unit 100.
0 is provided. The operation panel 50 is provided with an execution key for adjusting the transfer output (not shown). When the execution key for the transfer output adjustment process is pressed, the transfer output adjustment process is executed in the procedure described later. In the printer unit 200, the print head unit 20 uses the gradation data input from the read signal processing unit 9 to
A laser diode drive signal is generated, and the drive signal causes the semiconductor laser to emit light. The laser beam emitted from the print head unit 20 scans the surface of the photoconductor drum 23 by exposure through the mirrors 21 and 22. The surface of the photoconductor drum 23 is irradiated by the eraser lamp 24 before being exposed for each copy, and is uniformly charged by the charging charger 25. When exposed in this state, an electrostatic latent image of the original is formed on the photosensitive drum 23. Cyan, magenta, yellow, and black toner developing units 27 to 30
First, the cyan toner developing device 27 is selected,
The electrostatic latent image on the photosensitive drum 23 is developed. Suitable recording paper from the paper feed cassettes 31 to 33 is a timing roller pair 3.
It is transported to 4. The timing roller pair 34 transfers the recording paper to the transfer drum 40 at a timing when the front end of the toner image developed on the photosensitive drum 23 and the front end of the recording paper coincide with each other.
Transport to. The conveyed recording paper is sucked by the suction charger 35.
And the electrostatic attraction to the transfer drum 40 by the attraction roller 37. The pressing member 36 presses the transfer drum 40 in the direction of the suction roller 37 in order to bring the recording paper into close contact with the transfer drum 40 and to strongly suck the recording paper. The cyan toner image developed on the photoconductor drum 23 is transferred onto the recording paper wound on the transfer drum 40 by applying a predetermined voltage to the metal transfer roller 38 via the transfer film. It The pressing member 39 enhances the degree of contact between the recording paper and the photoconductor drum 23 and enhances the transferability.
0 is pressed toward the photoconductor drum 23. The toner remaining on the photoconductor drum 23 after the transfer of the toner image is removed by the cleaner 26. Subsequent to cyan, magenta, yellow, and black toner developing devices are sequentially selected, and the photoconductor drum 23 is charged, exposed, and toner-developed. The toner images of the respective colors developed on the photoconductor drum 23 are sequentially superimposed and transferred onto the recording paper wound around the transfer drum 40. The recording paper on which the toner images of four colors have been transferred is destaticized by the separation charge-eliminating charger 41, and then pushed up by the push-up member 42, and the tip of the pushed-up recording paper is caught by the separation claw 43. Thus, the transfer drum 40 is separated from the surface. The recording paper separated from the transfer drum 40 is fixed to the fixing device 4
After being heated and fixed through the sheet 4, the sheet is discharged to the tray 45.

The resistance value of the paper and the toner charge amount affect the transfer efficiency when the toner image visualized on the photosensitive drum 23 is transferred onto the recording paper. The characteristics of the recording paper and the toner charge amount will be described below. When the recording paper absorbs moisture or dries due to the surrounding environment, its electrical characteristics change. FIG. 2 is a graph showing the relationship between the volume resistance value (Ω · cm) of recording paper and the absolute humidity (g / m ³ ). As you can see from this graph, as the absolute humidity increases,
The volume resistance of the recording paper becomes low. FIG. 3 is a graph showing the relationship between the relative permittivity ε of paper and the absolute humidity (g / m ³ ). As can be seen from this graph, the relative permittivity ε of the paper increases as the absolute humidity increases and the volume resistance value of the paper decreases. Further, the toner charge amount before being transferred to the recording paper also changes depending on the humidity. FIG. 4 is a graph showing the relationship between the toner charge amount (μc / g) and the absolute humidity (g / m ³ ) before transfer. As can be seen from the graph, the higher the absolute humidity, the lower the toner charge amount before transfer. FIG. 5 shows that after the apparatus is left to stand for 7 to 8 hours in each of the three environments to adapt to the environment,
6 is a graph showing a transition of toner density when an image is output by changing a transfer output. The graph represented by the solid line shows a characteristic curve under the environment of a temperature of 23 ° C. and a humidity of 50% RH. When the transfer output is within the range of L1, the transfer efficiency is the best and the toner density on the recording paper is the maximum. The toner concentration gradually decreases after the transfer output exceeds about 400 μA. The graph represented by the dotted line shows a characteristic curve under the environment of a temperature of 18 ° C. and a humidity of 20% RH. Humidity 5
Compared to the case of 0% RH, the increase rate of the toner density with the increase of the transfer output is low, and the transfer efficiency is the best, that is, the value of the transfer output that maximizes the toner density is large. The toner density on the recording paper becomes maximum in the range where the transfer output is L2. The toner density gradually decreases from when the transfer output exceeds 550 μA as compared with the case where the humidity is 50% RH. The graph indicated by the alternate long and short dash line shows a temperature of 28 ° C and a humidity of 80%.
The characteristic curve in the environment of RH is shown. As can be understood from the graph, the increase rate of the toner density with the increase of the transfer output is higher than that in the case of the humidity of 50% RH, and the toner density sharply increases. As for the toner density, the transfer output is 100-
It becomes the maximum in the range of 200 μA, and the transfer output is 2
When the humidity exceeds 50 μA, the humidity drops more rapidly than when the humidity is 50% RH. As can be understood from the above three graphs, when the humidity is high, the rate of increase in toner density increases with the increase in transfer output, and the rate of decrease after reaching the maximum density also increases. Further, when the humidity is low, the increase rate of the toner density with the increase of the transfer output is low, and the decrease rate after the maximum density is reached is also low. Further, the range of transfer output where the maximum toner concentration can be obtained becomes wider when the humidity is lower. Continuing to refer to FIG. 5, the proper transfer output area at high humidity will be described. As shown in FIG. 5, when the humidity is high, such as 80% RH, the range of the transfer output where the toner density is maximum on the paper is extremely narrower than when the humidity is low. This is because the timing at which the toner density starts to decrease is early, especially on the high output side. This decrease in toner concentration on the high output side causes the toner charge amount to decrease in a high-humidity environment as shown in FIG. 4, and the toner applied to the transfer roller 38 via the transfer film has a reverse polarity. As a result of being charged to the recording paper, it is not transferred onto the recording paper and remains on the photoconductor drum 23. The reverse charging of the toner can be prevented by increasing the toner charge amount to some extent. Further, as shown in FIG. 2, the resistance value of the recording paper also decreases as the humidity increases, but when the resistance value is sufficiently high, the transfer output is suppressed to a low level,
Reverse charging of the toner can be suppressed.

FIG. 6 is a diagram showing a detailed structure around the photosensitive drum 23 and the transfer drum 40 of the copying machine in the embodiment. The same components as in FIG. 1 have the same reference numerals,
The duplicate explanation here is omitted. In the ROM 16 connected to the central processing unit (hereinafter referred to as CPU) 14,
The data of each control table described below is stored, and the RAM 13 temporarily stores the data necessary for executing the control process. An HV power source 212 that applies a predetermined voltage is connected to the transfer roller 38. Further, a pre-transfer charger 130 that raises the toner charge amount immediately before transfer is provided at a position immediately before the transfer portion. The charge wire current flowing through the pre-transfer charger 130 is 30
The grid voltage is fixed at 0 μA, and the grid voltage is controlled by the HV power supply 131 as necessary. During normal copying, the CPU 14 detects the absolute humidity (% RH) of the printer unit 200 by the environment sensor 15, and changes the voltage applied to the transfer roller 38 based on the result to keep the transfer efficiency constant. Table 1 shown below is a control table for specifying the applied voltage corresponding to the detected absolute humidity. This control table is a table used when forming a full-color image, and is stored in the ROM 16 together with various control data. As shown, the transfer output is set to increase as the absolute humidity decreases, based on the experimental data. The transfer output in each humidity section is set so that the second color is higher than the first color and the third color is higher than the second color. This considers the effect of charge-up of the transfer film due to the output of the previous color.

[Table 1]

When the execution key of the transfer output adjusting process provided on the operation panel 50 is pressed, the CPU 14 obtains the electrostatic capacity of the recording paper and the toner from the value of the current flowing in the transfer portion, and the toner before transfer is obtained from the obtained value. It is determined whether or not the charge amount of 1 is decreased and whether or not the resistance value of the recording paper is decreased. If the result of determination is that the charge amount of the pre-transfer toner is equal to or less than the appropriate value, the grid voltage of the pre-transfer charger 130 is increased to increase the charge amount of the pre-transfer toner.
When the electrostatic capacity and the resistance value of the recording paper are outside the appropriate values, the voltage applied to the transfer roller 38 is lowered by a predetermined amount. As a result, the toner that is reversely charged at the transfer portion and remains on the photoconductor is reduced. FIG. 7 is a flowchart of the process executed by the CPU 14 when the execution key for the transfer output adjustment process provided on the operation panel 50 is pressed. The details of the process will be described below in accordance with the flow of this flowchart with reference to the related drawings.
First, a reference toner pattern is formed at a position on the photoconductor drum 23 corresponding to the latter half position of the recording paper conveyed to the transfer drum 40 by a predetermined laser exposure amount, grid voltage, and developing bias (step S1). ). The transfer roller 38 starts to apply a voltage of a predetermined value immediately before the leading end of the recording paper wound around the transfer drum reaches the transfer portion, and stops applying the voltage after the end of the recording paper passes through the transfer portion. . 8A shows a state where the recording paper 502 has not reached the transfer portion yet, that is, a state where only the transfer film 503 exists between the transfer roller 38 and the photoconductor drum 23, and FIG. , Transfer roller 38 and photosensitive drum 2
3 shows a state in which the recording paper 502 and the transfer film 503 are present between the transfer roller 38 and the photosensitive drum 23, and (c) shows the toner layer 501, the recording paper 502, and the transfer film 503 present between the transfer roller 38 and the photosensitive drum 23. Indicates the state to do. CPU14
Measures the capacitance based on the value of the current flowing through the current measuring unit 214 at the timings shown in (a), (b) and (c) of FIG. 8 (step S2). FIG. 9 shows the photoconductor dielectric layer 500, the toner layer 501, the recording paper 502, the thickness d of the transfer film 503, the relative permittivity ε, and the capacitance C between the transfer roller 38 and the photoconductor drum 23. FIG. The value of the current flowing through the current measuring unit 214 depends on the electrostatic capacities C1 to C4 of the photoconductor dielectric layer 500, the toner layer 501, the recording paper 502, and the transfer film 503. The capacitance C per unit area is proportional to the relative permittivity ε / thickness d. That is, the current flowing through the current measuring unit 214 depends on the values of the thicknesses d1 to d4 and the relative dielectric constants ε1 to ε4. In this device, the transfer film 503 has a volume resistance value of 1
An insulating film of 0 ¹⁴ to 10 ¹⁵ Ω · cm is used. For this reason, even if a voltage is applied for current measurement, the electric charge only moves due to the polarization of each phase, and the free electric charge hardly flows. Therefore, the total capacitance when the layers are connected in series as a capacitor can be obtained from the measured current value. In the state of FIG. 8A, the capacitance C _a of the photoconductor dielectric layer 500 and the transfer film 503 in series is set.
Is measured. In the state of FIG. _8B, the capacitance C _b of the photoconductor dielectric layer 500, the recording paper 502, and the transfer film 503 in series is measured. In the state of FIG. 8C, the capacitance C _c of the photoconductor dielectric layer 500, the toner layer 501, the recording paper 502, and the transfer film 503 in series is measured. Figure 9
As shown in, the capacity of the photoconductor dielectric layer 500 is C1, the capacity of the toner layer 501 is C2, the capacity of the recording paper 502 is C3,
When the capacity of the transfer film 503 is represented by C4, the above _Ca ,
C _b and C _c satisfy the following expressions 1 to 3.

[Formula 1] C _a ^-1 = C1 ^-1 + C4 ^-1

## EQU2 ## C _b ^-1 = C1 ^-1 + C3 ^-1 + C4 ^-1

## EQU3 ## C _c ^-1 = C1 ^-1 + C2 ^-1 + C3 ^-1 + C4 ^{-1 The} reference toner pattern is created under the same exposure condition and the same development condition. The relative permittivity of the toner hardly changes with absolute humidity. On the other hand, the charge amount of the toner before transfer is
As shown in FIG. 4, it decreases as the absolute humidity increases. Therefore, the amount of developing toner on the photosensitive member changes as shown in the graph of FIG. 10 due to the change in absolute humidity. As a result, the thickness d2 of the toner layer 501 at the time of measuring the capacitance changes, and the capacitance changes. Therefore, by measuring the electrostatic capacity of the toner layer, the charge amount of the toner can be indirectly known. Therefore, the electrostatic capacitance C2 of the toner layer 501 is obtained by the following equation 4 based on the electrostatic capacitance value in each state measured in step S2 (step S).
3).

[Equation 4] C2 = (C _c ⁻¹ −C _b ⁻¹ ) ^{−1 When the} obtained electrostatic capacitance C2 of the toner layer 501 is the reference value C2 _ref (= 20 pf) stored in the ROM 16 or more, (YES in step S4), it is determined that the developed toner (before transfer) has a low charge amount, the toner is reversely charged by the transfer output, and is likely to remain on the photosensitive drum 23. The grid voltage of the charger 130 is increased by a predetermined amount from the value normally used to raise the toner charge amount (step S5). Specifically, ROM
The grid voltage of the pre-transfer charger 130 is determined with reference to the control table shown in Table 2 stored in 16. The obtained electrostatic capacity C2 of the toner layer 501 is the reference value C2.
If it is less than _ref (= 20 pf) (step S4)
NO), the control of the grid voltage of the pre-transfer charger 130 is skipped.

[Table 2] By controlling the grid voltage as described above, the charge amount of the toner before transfer is increased, and even when the transfer output is high, the toner is charged to the opposite polarity in the transfer portion,
It can be prevented from remaining on the photosensitive drum 23. As a result, the relationship between the transfer output and the toner density is corrected as shown by the one-dot chain line in FIG.
It becomes possible to obtain stable transfer efficiency. On the other hand, the electrostatic capacity C3 of the recording paper 502 is affected by the change in the relative permittivity accompanying the change in the absolute humidity as shown in FIG.
Further, as described above, since the resistance value of the recording paper 502 also changes depending on the absolute humidity, the change in the resistance value can be indirectly known by detecting the capacitance C3. Therefore, based on the values of the capacitances C _a , C _b , and C _c in each state measured in step S2, the capacitance C3 of the recording paper 502 is calculated by the following equation 5 (step S6).

[Equation 5] C3 = (C _b ⁻¹ + C _a ⁻¹ ) ^{−1 If the} obtained capacitance C3 of the recording paper 502 is equal to or _larger than the reference value C3 _ref (YES in step S7), as shown by the arrow in FIG. In addition, the HV power supply 2 is set so that the voltage applied to the transfer roller 38 is lowered by a predetermined amount from the currently set value.
12 is controlled (step S8). Specifically, the relationship between the absolute humidity and the transfer output in the transfer output control table shown in Table 1 is shifted to a value one step lower. For example, the value of the transfer output corresponding to the absolute humidity is reduced by 0.2 as a whole. When the electrostatic capacity C3 of the recording paper 502 is less than the reference value C3 _ref (NO in step S7), the process ends.

(2) Modified Example A modified example of the transfer output adjusting process executed by the CPU 14 when the execution key of the transfer output adjusting process provided on the operation panel 50 is pressed will be described below. In the modified example of the transfer output adjusting process, the process flow itself is the same as the flowchart shown in FIG. 7, but the formation content of the reference toner pattern (the process corresponding to step S1 in FIG. 7) is different. Therefore, the timing for measuring the electrostatic capacitance (the process corresponding to step S2 in FIG. 7), the formula used to obtain the electrostatic capacitance C2 of the toner layer 501 from the measured value of the electrostatic capacitance, and the recording paper 502. The formulas used to determine the electrostatic capacitance C3 of are different. The contents of the output control of the pre-transfer charger 130 and the transfer roller 38 based on the obtained electrostatic capacitance C2 of the toner layer 501 and electrostatic capacitance C3 of the recording paper 502 are the same as in the transfer output adjustment process. Hereinafter, this difference will be described. FIG. 13 is a flowchart executed by the CPU 14 in the modified example of the transfer output adjusting process. In the modification of the transfer output adjusting process, the toner image formed on the photoconductor drum 23 is directly transferred onto the transfer film by a predetermined laser exposure amount, grid voltage, and developing bias (step S10). The CPU 14 is shown in FIG.
(A), when the recording paper 502 has not reached the transfer portion, that is, the transfer roller 38 and the photosensitive drum 23.
The transfer film 503 exists between the transfer roller 38 and the photosensitive drum 23 as shown in (b), and the transfer film 503 exists between the transfer roller 38 and the photosensitive drum 23. As shown, at the timing when the recording paper 502 and the transfer film 503 are present between the transfer roller 38 and the photoconductor drum 23, the capacitance is measured from the current value flowing through the current measuring means 214 (step S11). Here, in the state of FIG. 14A, the capacitance C ′ _a of the photoconductor dielectric layer 500 and the transfer film 503 in series is measured. In the state of FIG. 14B, the capacitance C ′ _b of the photoconductor dielectric layer 500, the toner layer 501, and the transfer film 503 in series is measured. Figure 1
In the state of (c) of 4, the photoconductor dielectric layer 500, the recording paper 5
02, the capacity C ′ _{c of} the transfer film 503 in series is measured. As in the case of the transfer output adjusting process, the capacitance of the photoconductor dielectric layer 500 is C1, and the capacitance of the toner layer 501 is C.
2, C3 a capacity of the recording sheet 502, to represent the capacity of the transfer film 503 in C4, the _{C 'a, C' b,} C 'c satisfy the relationship of the following numbers 6 to Equation 8.

## EQU6 ## _C'a ^-1 = C1 ^-1 + C4 ^-1 = C _a ^-1

## EQU7 ## _C'b ^-1 = C1 ^-1 + C2 ^-1 + C4 ^-1

## EQU8 ## _C'c ^-1 = C1 ^-1 + C3 ^-1 + C4 ^-1 = C _b ^{-1 From the} above Equations 6 to 8, the following Equation 9 is used to calculate the toner layer 50:
The capacitance C2 of 1 is calculated (step S12).

C2 = (C ′ _b ⁻¹ −C ′ _a ⁻¹ ) ^{−1 If the} calculated electrostatic capacitance C2 of the toner layer 501 is greater than or equal to a predetermined reference value C2 _ref (YE in step S13)
S): It is determined that the toner has deteriorated and the charge amount of the toner before the transfer has decreased, and the grid voltage of the pre-transfer charger 130 is increased by a predetermined amount from the normally used value to increase the toner charge amount. (Step S14). When the calculated value of the electrostatic capacity C2 of the toner layer 501 is less than the predetermined reference value C2 _ref (N in step S13)
O), the process proceeds to the next step S15 without controlling the output of the pre-transfer charger 130. Further, the electrostatic capacity C3 of the recording paper 502 is calculated using the following formula 10 (step S
15).

[Equation 10] C3 = (C ′ _c ⁻¹ −C ′ _a ⁻¹ ) ^{−1 If the} calculated electrostatic capacitance C3 of the recording paper 502 is greater than or equal to a predetermined reference value C3 _ref (YE in step S16)
S), the resistance value of the recording paper 502 has decreased, and it is determined that the reverse charging of the toner is likely to occur in the transfer portion, and the voltage applied to the transfer roller 38 is decreased by a predetermined amount (step S17). . When the calculated value of the electrostatic capacity C3 of the recording paper 502 is less than the predetermined reference value C3 _ref (NO in step S16), the output control of the transfer roller 38 is not performed, and the process ends. Although the transfer roller 38 is used in the copying machine of the present embodiment, the same effect can be obtained by using a transfer brush or the like. Also,
A transfer belt may be used instead of the transfer drum 40.

[0011]

In the image forming apparatus of the present invention, the electrostatic capacity between the member for applying the transfer charge to the transfer film and the photosensitive member is detected by the measuring means at a predetermined timing, and the value of the detected electrostatic capacity Indirectly check the resistance value of the recording paper and the deterioration state of the toner. Thereby, the transfer conditions can be controlled appropriately. Further, since the resistance value of the recording paper and the deterioration state of the toner are checked only by the measured value by the measuring means, the device can be simplified.

[Brief description of drawings]

FIG. 1 is a sectional view of a digital full-color copying machine according to an embodiment.

FIG. 2 is a graph showing the relationship between the volume resistance value (Ω · cm) of recording paper and the absolute humidity (g / m ³ ).

FIG. 3 is a graph showing a relationship between relative permittivity ε of paper and absolute humidity (g / m ³ ).

FIG. 4 Toner charge amount before transfer (μc / g)
2 is a graph showing the relationship between the absolute humidity and the absolute humidity (g / m ³ ).

FIG. 5 is a schematic diagram showing a system in which the devices are operated under three environments.
6 is a graph showing a transition of toner density when an image is output by changing a transfer output after being left for 8 hours to adapt to an environment.

FIG. 6 is a diagram showing a detailed configuration around a photosensitive drum and a transfer drum of the copying machine in the embodiment.

FIG. 7 is a flowchart of a transfer output adjustment process executed by a CPU.

8A to 8C are diagrams showing three states between a transfer roller and a photosensitive drum.

FIG. 9 is a diagram showing a relationship between respective thicknesses of a dielectric layer of a photoconductor, a toner layer, recording paper, and a transfer film and electrostatic capacities C1 to C4.

FIG. 10 is a graph showing the amount of toner adhering to the photoconductor when the toner charge amount changes due to a change in absolute humidity.

FIG. 11 is a graph showing the relationship between transfer output and toner concentration.

FIG. 12 is a graph showing the relationship between transfer output and toner concentration.

FIG. 13 is a flowchart of a modified example of the transfer output adjustment processing executed by the CPU.

14A to 14C are diagrams showing three states between a transfer roller and a photosensitive drum.

[Explanation of symbols]

13 ... RAM 14 ... CPU 15 ... Environment sensor 16 ... ROM 23 ... Photosensitive drum 31-33 ... Paper feed cassette 38 ... Transfer roller 40 ... Transfer drum 130 ... Charger before transfer 131, 212 ... HV power supply 214 ... Current measuring unit

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Claims (4)

(57) [Claims] 1. An image forming apparatus adopting an electrophotographic system, comprising: a photoconductor, a developing unit that forms a reference toner pattern on the photoconductor, and a transfer unit that transfers the reference toner pattern on the photoconductor onto a recording sheet. , A transfer film provided between the photoconductor and the transfer means, a pre-transfer charger that raises the charge amount of the toner image before the toner image is transferred to the recording paper, and a photosensitive material through the transfer film and the recording paper. A first capacitance between the body and the transfer means, and a second capacitance between the photoreceptor and the transfer means via the transfer film, the recording paper and the reference toner pattern.
And a first calculating unit that calculates the capacitance of the reference toner pattern according to the first and second capacitances measured by the measuring unit, and The first comparing means for comparing the capacitance of the reference toner pattern calculated by the calculating means with the first reference value, and the capacitance of the reference toner pattern calculated by the first calculating means are the first When it is judged that it is more than the standard value of
An image forming apparatus comprising: first control means for increasing the grid voltage of the pre-transfer charger by a predetermined amount. 2. The measuring means further measures a third capacitance between the photoconductor and the transfer means via only a transfer film, and according to the first and third capacitances, Second calculating means for calculating the electrostatic capacity of the recording paper; second comparing means for comparing the electrostatic capacity of the recording paper calculated by the second calculating means with a second reference value; Further comprising second control means for reducing the voltage applied to the transfer means by a predetermined amount when it is determined that the electrostatic capacity of the recording paper calculated by the calculation means is equal to or larger than the second reference value. The image forming apparatus according to claim 1, wherein: 3. An image forming apparatus adopting an electrophotographic system, comprising: a photoconductor, a developing unit for forming a reference toner pattern on the photoconductor, and a transfer unit for transferring the reference toner pattern on the photoconductor onto a recording sheet. , A transfer film provided between the photoconductor and the transfer means, a pre-transfer charger that raises the charge amount of the toner image before the toner image is transferred to the recording paper, and a photoconductor through the transfer film only. Measuring means for measuring a first capacitance between the transfer means and a second capacitance between the photoconductor and the transfer means via the transfer film and the reference toner pattern, and the measuring means. First calculation means for calculating the capacitance of the reference toner pattern according to the first and second calculated capacitances, and the capacitance of the reference toner pattern calculated by the first calculation means and the first calculation means. Standard of 1 When it is determined that the electrostatic capacity of the reference toner pattern calculated by the first calculating means and the first comparing means is compared with the first reference electrostatic capacity or more, the grid voltage of the pre-transfer charger And a first control unit that increases the predetermined amount by a predetermined amount. 4. The measuring means further measures a third capacitance between the photoconductor and the transfer means via the transfer film and the recording paper, and the first and third measured capacitances are measured by the measuring means. Second calculating means for calculating the electrostatic capacity of the recording sheet according to the electrostatic capacity, and second calculating means for comparing the electrostatic capacity of the recording sheet calculated by the second calculating means with a second reference value. And a second control unit that lowers the voltage applied to the transfer unit by a predetermined amount when it is determined that the electrostatic capacity of the recording paper is equal to or larger than the second reference value. The image forming apparatus according to claim 3 .